A device of that kind is known, for example, from German Patent No. 101 35 142 and is used, for example, in the intake system of an internal combustion engine in order to determine the air mass flow delivered to the internal combustion engine through a line. The known device has a channel structure with an inlet region from which a measuring channel, provided with the measuring element, branches off. The inlet region has a separation zone with at least one separation aperture situated at a side wall of the part of the device inserted into the line. The separation zone serves to remove liquid particles and/or solid particles from the channel structure, thus preventing them from entering the measuring channel which is provided with the measuring element, and contaminating the measuring element.
The edges formed by the front side facing toward the main direction of flow and the side walls of the part of the device inserted into the line are to be regarded as leading edges where, when the device is used in the medium-carrying line, large areas of detached flow develop which may give rise, on the one hand, to great pressure losses and, on the other hand, to unintended pulsation of the flow, as a result of which pressure variations are transmitted from the separation aperture through the separation zone to the inlet region and, from there, also to the measuring channel which branches off from the inlet region. The pressure variations in the measuring channel may cause considerable falsification of the output signal of the measuring element.